Post cards and letters for delivery by the Postal Service commonly are used in the transmission of messages, data, information, and the like. When it is desired to maintain the confidentiality of the information, an envelope often is employed to hide the message from view by everyone except the recipient. The information, or message may be contained on a separate sheet inserted in the envelope, or applied directly to an interior surface of the envelope. Envelope blanks are available upon which the message first may be applied, after which the blank is folded to form an envelope with the message at an inside surface thereof hidden from view. As is understood, envelopes to be mailed must bear letter rate postage which is, of course, greater than post card rate postage. Double post cards are available which include mailing and return post card sections connected along a fold line. However, the sections generally are not sealed, or closed, about the entire periphery of the card sections, thereby allowing inspection of any message contained at the inside facing surfaces thereof. In brief, prior art post cards provide a price advantage over letters in the cost of mailing, and often in the cost of production, but lack the privacy afforded by the use of an envelope to contain the message.